What you are looking at is a crab:

Specifically, it is a carrier crab, they live in the Indian ocean and they have formed a unique partnership with Long-spined Sea Urchins.

The crab uses two of its legs to hold on to the sea urchin while the other two do the walking, the claws are kept at the ready.

Seas urchins have long spines and can painfully poke any predators that come nearby. It also gives the crab easy covering when it is moving across long flat sea beds, when it is at its most vulnerable.

In return for giving this shielding to the crab, the sea urchin, which is terribly slow, is given fast transport to new, ripe feeding areas, which the crab naturally gravitates to anyways.

These relationships have been in place for tens of thousands of years and continue to this day. Another incredible example of symbiosis.